A fabricated bioporous reactive wall-barrier wall for a contaminated site

Abstract

The application discloses a kind of assembled bioporous reaction wall-barrier wall for contaminated site, including the assembled bioporous reaction wall of the positive front of pollution plume diffusion direction and the assembled barrier wall of nested arrangement in its outer periphery, both vertical to the flow direction of groundwater;Assembled bioporous reaction wall is obtained by transverse, longitudinal continuous splicing assembly from multiple bioporous reaction wall components;Assembled barrier wall is obtained by transverse, longitudinal continuous splicing assembly from multiple barrier wall board components;Bioporous reaction wall component is the box of internal cavity, the surface of box perpendicular to flow direction is arranged geocomposite drainage net and internal cavity is communicated, and cavity fills zero-valent iron-biochar reinforced / immobilized sulfate-reducing bacteria reactivity filler.The application can realize soil pollution remediation while realizing the control of contaminated site, and can be freely assembled and disassembled according to the pollution plume range of contaminated site, and construction maintenance is convenient.

Description

Technical Field

[0001] This invention relates to the field of groundwater pollution remediation and control technology for complex contaminated sites, and particularly to a prefabricated bio-permeable reactive barrier wall for contaminated sites. Background Technology

[0002] Soil pollutants migrate to deeper layers and enter aquifer systems through leaching and transport, becoming a major source of groundwater pollution. The maximum migration depth of pollutants from industrial and agricultural contaminated sites can reach over 30 meters.

[0003] Vertical barrier wall technology is one of the most commonly used and effective methods for controlling soil and groundwater pollution. However, the permeability coefficient of traditional cement-based barrier walls is typically around 1×10⁻⁶. -4 Up to 1×10 -6 Within the range of cm / s, cement is susceptible to chemical erosion by sulfates, leading to a rapid increase in material permeability. Simultaneously, cement production results in high energy and raw material consumption and carbon dioxide emissions. While traditional bentonite-based barrier walls exhibit excellent impermeability under mild chemical conditions, their permeability coefficient often increases by several orders of magnitude in multi-component contaminated sites, making long-term effective control difficult.

[0004] Permeable reactive barrier (PRB) technology is widely used for soil-groundwater remediation of sites contaminated with both heavy metals and organic pollutants due to its advantages such as continuous in-situ treatment of multiple pollutants, simple principle, good treatment effect, and high cost-effectiveness, aiming to achieve efficient, clean, and inexpensive remediation. Although PRBs demonstrate satisfactory performance in pollutant removal, they still suffer from reactive losses, mineral precipitation and clogging leading to reduced permeability, and low efficiency in treating large-area pollutant plumes during long-term use. The reduced hydraulic conductivity of the PRB can affect groundwater flow direction, altering the water's residence time within the barrier and causing bypass phenomena.

[0005] Existing contaminated site management and soil remediation technologies are typically implemented independently, without being combined to achieve integrated management and remediation. Developing combined management and remediation technologies is a trend in soil pollution remediation. Most existing barrier walls and permeable reactive walls employ single structures and fabrication methods, while some utilize prefabricated structures and construction techniques. There are also cases involving combined barrier wall-permeable reactive wall structures, but the following shortcomings remain: (1) Traditional vertical barrier wall materials have high permeability and low compatibility.

[0006] (2) The permeable reactive wall material has a rapid decrease in permeability coefficient and low efficiency in treating large-area pollution plumes.

[0007] (3) The rock strata in the polluted area are complex and the pollutants migrate deep.

[0008] (4) Problems such as the inability to combine contaminated site control and remediation technologies. Summary of the Invention

[0009] To address the shortcomings of existing technologies, this invention proposes a prefabricated bio-permeable reactive barrier wall for contaminated sites, which is particularly suitable for emergency containment and can remediate and contain contamination in a short period of time.

[0010] The specific technical solution is as follows: A prefabricated bio-permeable reactive barrier for contaminated sites includes a prefabricated bio-permeable reactive barrier and a prefabricated barrier wall arranged perpendicular to the direction of groundwater flow; the prefabricated bio-permeable reactive barrier is arranged in the direction of the main groundwater flow; the prefabricated barrier wall is nested around the prefabricated bio-permeable reactive barrier and fixed to an impermeable layer at its bottom. The prefabricated bio-permeable reactive wall is assembled by continuously splicing multiple bio-permeable reactive wall components horizontally and vertically; the prefabricated barrier wall is assembled by continuously splicing multiple barrier wall panel components horizontally and vertically; the horizontal direction is horizontal and the vertical direction is vertical. The bio-permeable reactive wall component is a box with an internal cavity. A geotextile drainage net is arranged on the surface of the box perpendicular to the water flow direction and communicates with the internal cavity. The internal cavity of the box is filled with zero-valent iron-biochar-enhanced / immobilized sulfate-reducing bacteria reactive filler.

[0011] Furthermore, the bio-permeable reactive wall component includes: a tenon, a slot, and a geotextile drainage net; the two planes of the box body of the bio-permeable reactive wall component used for lateral connection are provided with a tenon structure, that is, one plane is provided with a protruding tenon and the other plane is provided with a recessed slot.

[0012] Furthermore, the barrier wall panel component includes: a second tenon and a second slot; the barrier wall panel component is in the form of a rectangular block structure, and its two planes perpendicular to the horizontal direction are also provided with mortise and tenon structures, that is, one plane is provided with a protruding second tenon, and the other plane is provided with a concave second slot.

[0013] Furthermore, the barrier wall panel components are made of materials including: slag, polymer-modified bentonite, and geopolymer.

[0014] Furthermore, the mass ratio of the slag soil is 55% to 85%, the mass ratio of polymer-modified bentonite is 5% to 15%, and the mass ratio of geopolymer is 10% to 30%.

[0015] Furthermore, the joints between adjacent bio-permeable reactive wall components, the joints between adjacent barrier wall panel components, and the joints between bio-permeable reactive wall components and barrier wall panel components are sealed by injecting calcium-based bentonite slurry.

[0016] A method for constructing a prefabricated bio-permeable reactive barrier wall for contaminated sites includes the following steps: S1: Prepare zero-valent iron-biochar-enhanced / immobilized sulfate-reducing bacteria reactive filler, fill it into the internal cavity of the bio-permeable reactive wall component, and then encapsulate it with geotextile composite drainage net to obtain the bio-permeable reactive wall component. S2: Prepare barrier wall panel components, the materials of which include: slag, polymer-modified bentonite, and geopolymer; in the barrier wall panel components, the mass proportion of slag is 55%~85%, the mass proportion of polymer-modified bentonite is 5%~15%, and the mass proportion of geopolymer is 10%~30%; S3: A channel-type cutting trench is opened downstream of the pollution plume using the channel-type cutting underground continuous wall construction process. S4: Assemble a positioning guide frame for the channel-type cutting groove, and slowly insert the barrier wall panel components or bio-permeable reactive wall components into the channel-type cutting groove and fix them in sequence according to the design drawings, thereby completing the prefabricated bio-permeable reactive wall-barrier wall for contaminated sites as described in any one of claims 1-6.

[0017] Further, in S1, the zero-valent iron-biochar-enhanced / immobilized sulfate-reducing bacteria reactive packing material is prepared through the following sub-steps: (1.1) Pyrolyze wheat straw at 700-750℃ to form biochar, then sterilize the biochar in an immobilization medium at 120-122℃ for 30-40 min, inoculate sulfate-reducing bacteria at an inoculum concentration of 2%-2.1% by mass, and incubate at 25-30℃ and 120-180 r•min. -1 Under fixed conditions, culture for 18-24 hours; (1.2) Stir the substances in the culture medium at 6000-8000 r•min -1 Centrifuge for 10-15 min, discard the supernatant, and wash the lower precipitate with physiological saline. Centrifuge the washed product again at 3000-5000 r / min for 10 min, and take the lower precipitate and wash it at least 3 times. The resulting solid is the biochar-enhanced / immobilized sulfate-reducing bacteria. (1.3) Biochar-enhanced / immobilized sulfate-reducing bacteria and zero-valent iron are stirred at a mass ratio of 4:1 for 30-40 min at high speed to obtain zero-valent iron-biochar-enhanced / immobilized sulfate-reducing bacteria reactive filler. This filler is then inserted into the internal cavity of the biopermeable reactive wall component, ensuring that the permeability coefficient is greater than 1×10⁻⁶.-3 cm / s.

[0018] Furthermore, in step S2, the barrier wall panel component is prepared through the following sub-steps: (2.1) Mix sodium polyacrylate bentonite and water thoroughly for 30-60 minutes. Seal the resulting sodium polyacrylate bentonite slurry in a container and let it stand until it is completely hydrated. Then add a certain mass of construction waste and stir at 3000 r / min for 30-60 minutes. (2.2) Add magnesium oxide and blast furnace slag to the slurry prepared in step (2.1), and stir for 30-60 minutes to obtain a mixed slurry of slag, polymer-modified bentonite, and geopolymer; pour the mixed slurry into a mold, press it into shape, and then cure it. After standing for 24 hours, the barrier wall panel component is obtained, and its permeability coefficient is less than 1×10. -7 cm / s.

[0019] Furthermore, the channel-cutting diaphragm wall construction process is a construction technique that uses a chainsaw to rotate up and down and move horizontally along the pre-set prefabricated bio-permeable reactive wall-barrier wall layout direction to cut channel-cutting grooves in the foundation soil layer.

[0020] The beneficial effects of this invention are: (1) This invention combines green remediation of pollution and risk management of vertical pollution barrier. The prefabricated bio-permeable reactive barrier can be effectively applied to scenarios where pollutants migrate deeply in regional contaminated sites and the sites are located in highly heterogeneous soils or loose soil layers (such as sand and gravel strata). The prefabricated bio-permeable reactive barrier can effectively intercept the pollution plume and guide the multi-component pollutants in the pollution plume to react with the reactive filler, thereby achieving the effect of remediation. This invention is convenient to construct and maintain, and is particularly suitable for emergency barrier, enabling pollution remediation and barrier in a short period of time.

[0021] (2) The zero-valent iron-biochar enhanced / immobilized sulfate-reducing bacteria reactive packing used in this invention has superior overall remediation performance and lower packing replacement and disposal frequency. It is more environmentally friendly and low-carbon, and can alleviate potential remediation problems caused by dominant flow channels in heterogeneous sites. It has great potential in the remediation of groundwater pollution such as trichloroethylene, petroleum, and chromium.

[0022] (3) The prefabricated barrier wall used in this invention has high impermeability, high mechanical strength, strong chemical compatibility, and is green, low-carbon, and environmentally friendly. The permeability coefficient can be maintained at 1×10 during long-term service. -7 Below cm / s.

[0023] (4) The prefabricated bio-permeable reactive wall-barrier wall combination structure used in this invention can determine the range of the reactive zone and the barrier zone according to the range of the pollution plume of the specific contaminated site, and can be freely assembled and disassembled, making construction and maintenance convenient. Attached Figure Description

[0024] Figure 1 This is a schematic diagram of the prefabricated bio-permeable reactive barrier wall used for contaminated sites in an embodiment of the present invention.

[0025] Figure 2 This is a schematic diagram of the structure of the barrier wall panel component and the permeable reaction chamber component in the embodiment of the present invention, wherein (a) is the barrier wall panel component and (b) is the permeable reaction chamber component.

[0026] Figure 3 This is a diagram showing the Darcy flow field results using a traditional pure barrier wall scheme.

[0027] Figure 4 This is a Darcy flow field result diagram of the prefabricated bio-permeable reactive wall-barrier wall scheme according to an embodiment of the present invention.

[0028] In the diagram, the components of the bio-permeable reactive wall are: component 1, tenon 1-1, slot 1-2, and geotextile composite drainage net 1-3; and component 2 of the barrier wall panel, tenon 2-1 and slot 2-2. Detailed Implementation

[0029] The present invention will be described in detail below with reference to the accompanying drawings and preferred embodiments. The objectives and effects of the present invention will become clearer as a result. The present invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.

[0030] The soil structure of a contaminated site, from top to bottom, includes: topsoil, groundwater layer, and bedrock. Pollution sources exist within the topsoil layer, and pollutants move and diffuse from these sources to surrounding areas via groundwater, forming a specific contaminated area, known as a pollution plume.

[0031] To prevent the spread of contamination plumes, this embodiment proposes a prefabricated biopermeable reactive barrier for contaminated sites, such as... Figure 1 As shown, the system includes prefabricated biopermeable reactive barriers and prefabricated barrier walls positioned perpendicular to the groundwater flow direction. The prefabricated biopermeable reactive barriers are positioned directly in front of the contamination plume to block the spread of contaminants from the surface soil and groundwater layers, and to continuously treat contaminants in situ. The prefabricated barrier walls are nested around the prefabricated biopermeable reactive barriers, with their bottoms extending into the bedrock to a certain depth, forming a full-section seepage barrier. The prefabricated biopermeable reactive barriers and prefabricated barrier walls are continuously assembled to form a continuous underground wall with contamination plume interception and soil remediation functions.

[0032] The prefabricated bio-permeable reactive wall is assembled by continuously splicing multiple bio-permeable reactive wall components 1 horizontally and vertically; the prefabricated barrier wall is assembled by continuously splicing multiple barrier wall panel components 2 horizontally and vertically; where horizontal refers to the horizontal direction and vertical refers to the vertical direction. The joints between adjacent bio-permeable reactive wall components 1, adjacent barrier wall panel components 2, and the joints between bio-permeable reactive wall components 1 and barrier wall panel components 2 are sealed by injecting calcium-based bentonite slurry.

[0033] The modular design of the components enhances the adaptability of the diaphragm wall to different soil types (suitable for artificial fill, cohesive soil, silt, gravel, etc.), improves dynamic adjustment capabilities, and allows for free assembly and disassembly, facilitating construction and maintenance. The prefabricated design also improves construction efficiency and reduces construction costs.

[0034] like Figure 2 As shown, the biopermeable reactive wall component 1 includes: tenon 1-1, slot 1-2, and geotextile drainage mesh 1-3. The biopermeable reactive wall component 1 is a box-like structure with an internal cavity. The box has mortise and tenon joints on two planes perpendicular to the horizontal direction; one plane has a protruding tenon 1-1, and the other plane has a recessed slot 1-2. The geotextile drainage mesh 1-3 is arranged on the surface of the box perpendicular to the water flow direction and communicates with the internal cavity. The internal cavity is filled with zero-valent iron-biochar-enhanced / immobilized sulfate-reducing bacteria reactive filler (where / indicates "or"), used to improve the removal efficiency of pollutants through physical, chemical, and biological synergistic effects, especially performing well in the remediation of heavy metals and organic pollution.

[0035] Laterally adjacent biopermeable reactive wall components 1 are connected by a mortise and tenon structure, that is, the tenon-1-1 of one biopermeable reactive wall component 1 engages with the slot-1-2 of another biopermeable reactive wall component 1 to achieve a stable connection. Between longitudinally adjacent biopermeable reactive wall components 1, the lower surface of the upper biopermeable reactive wall component 1 is attached to the upper surface of the lower biopermeable reactive wall component 1, and is sealed and further fixed by calcium-based bentonite slurry.

[0036] The barrier wall panel component 2 includes: tenon 2-1 and slot 2-2. The barrier wall panel component 2 has a rectangular block structure, and its two planes perpendicular to the horizontal direction also have mortise and tenon structures; one plane has a protruding tenon 2-1, and the other plane has a recessed slot 2-2. The material of the barrier wall panel component 2 includes slag, polymer-modified bentonite, and geopolymer, all of which are below 200 mesh. The slag accounts for 55%~85% of the mass, the polymer-modified bentonite accounts for 5%~15%, and the geopolymer accounts for 10%~30%. This material ratio gives the material high impermeability, high mechanical strength, strong chemical compatibility, and is green, low-carbon, and environmentally friendly. The permeability coefficient can be maintained at 1×10⁻⁶ during long-term service. -7 Below cm / s.

[0037] Laterally adjacent barrier wall panel components 2 are connected by a mortise and tenon structure, that is, the tenon 2-1 of one barrier wall panel component 2 engages with the slot 2-2 of another barrier wall panel component 2 to achieve a stable connection. Between longitudinally adjacent barrier wall panel components 2, the lower surface of the upper barrier wall panel component 2 is attached to the upper surface of the lower barrier wall panel component 2, and is sealed and further fixed by calcium-based bentonite slurry.

[0038] To prepare the prefabricated biopermeable reactive barrier for contaminated sites, this embodiment also proposes a construction method for the prefabricated biopermeable reactive barrier for contaminated sites, including the following steps: S1: Preparation of biopermeable reactive wall component 1, wherein the zero-valent iron-biochar-enhanced / immobilized sulfate-reducing bacteria reactive filler is prepared through the following sub-steps: (1.1) Pyrolyze wheat straw at 700-750℃ to form biochar, then sterilize the biochar in an immobilization medium at 120-122℃ for 30-40 min, inoculate sulfate-reducing bacteria at an inoculum of 2%-2.1% (mass fraction), and incubate at 25-30℃ and 120-180 r•min. -1 Under fixed conditions, culture for 18-24 hours.

[0039] (1.2) Stir the substances in the culture medium at 6000-8000 r•min -1 Centrifuge for 10-15 min, discard the supernatant, and wash the lower precipitate with 1%-1.1% (mass fraction) physiological saline. Centrifuge the washed product again at 3000-5000 r / min for 10 min, take the lower precipitate and repeat the washing 3 times. The resulting solid is the biochar-enhanced / immobilized sulfate-reducing bacteria.

[0040] (1.3) Biochar-enhanced / immobilized sulfate-reducing bacteria and zero-valent iron are stirred at a mass ratio of 4:1 for 30-40 minutes to obtain zero-valent iron-biochar-enhanced / immobilized sulfate-reducing bacteria reactive packing. This packing is then filled into the internal cavity of the biopermeable reactive wall component 1, and the permeability coefficient of the reactive packing is greater than 1×10⁻⁶. -3 cm / s.

[0041] S2: Prepare barrier wall panel component 2, which is specifically prepared through the following sub-steps: (2.1) Mix a certain mass of sodium polyacrylate bentonite and water thoroughly for 30-60 minutes. Seal the resulting sodium polyacrylate bentonite slurry in a container and let it stand for 24 hours. After it is fully hydrated, add a certain mass of construction waste and stir at high speed (3000 r / min) for 30-60 minutes.

[0042] (2.2) Add a certain mass of magnesium oxide and blast furnace slag (i.e., geopolymer) to the slurry prepared in step (2.1), and stir for 30-60 minutes to obtain a mixed slurry of slag, polymer-modified bentonite, and geopolymer. The mass ratio of each raw material should meet the following requirements: the mass ratio of slag in the mixed slurry is 55%~85%, the mass ratio of polymer-modified bentonite is 5%~15%, and the mass ratio of geopolymer is 10~30%. Pour the mixed slurry into a mold, press it into shape, and then cure it. After standing for 24 hours, the barrier wall panel component 2 is obtained, and its permeability coefficient meets the requirement of being less than 1×10⁻⁶. -7 cm / s.

[0043] S3: A channel-type cutting trench is created downstream of the pollution plume using a diaphragm wall construction technique. Specifically, based on the established coordinate reference points of the diaphragm wall, layout and elevation measurements are performed according to the design drawings. When constructing a single side, the endpoints of both transverse sides of the diaphragm wall need to be laid out along the retaining axis (i.e., the central axis of the planned channel-type cutting trench) to ensure accuracy and verification. Using a total station, the channel-type cutting pile driver is adjusted to the appropriate position. A cutting box equipped with a cutting chain and cutter head, meeting the design depth (at least to the bedrock), is inserted into the ground for longitudinal cutting and transverse advancement to form the channel-type cutting trench.

[0044] The channel-cutting underground continuous wall construction technology can solve the problem of vertical prevention and remediation of contaminated sites with complex rock strata and deep pollutant migration, and the wall depth can reach 90m.

[0045] S4: Assemble the positioning guide frame and fix it on both sides of the channel-type cutting groove using a level to ensure stable placement on the bottom. This is used for positioning and verticality control during the insertion of the bio-permeable reactive wall component 1 and the barrier wall panel component 2. According to the design drawings, slowly insert the barrier wall panel component 2 or the bio-permeable reactive wall component 1 into the channel-type cutting groove using a crawler crane and fix it in the positioning frame, ensuring that the connection method between each component follows the design requirements; repeat this process to complete the prefabricated bio-permeable reactive wall-barrier wall.

[0046] The present invention will now be described in detail through examples and comparative examples.

[0047] The contaminated site was identified as the old factory area of ​​a pharmaceutical company. The company's main products and raw materials include ephedrine and fluoride series. Anomalies were observed in the factory's water quality data. Following investigation by relevant departments, environmental pollution was found due to groundwater leakage in parts of the riverside area of ​​the industrial park. Benzene was found to be the most severely contaminated pollutant among all detected pollutants. Therefore, benzene was selected as a representative pollutant to predict its spatiotemporal transport in the groundwater within the study area and to evaluate the pollution prevention performance of different vertical barrier systems applied to the study area.

[0048] Comparative example: A traditional pure barrier wall solution is adopted, with the barrier wall structure located 100m downstream of the factory area, embedding the wall into an impermeable layer (i.e., Figure 1 The bedrock in the middle is 1m thick, the vertical barrier wall is 150m long on one side, the barrier wall is 1m thick, and the permeability coefficient is 5×10⁻⁶. -11 The aquifer has a flow rate of m / s and a porosity of 0.35. Other parameters are: a benzene source concentration of 1000 mg / L and a benzene degradation coefficient in the aquifer of 10. -9 s -1 The hindering factor in the vertical barrier wall is 17.88. The horizontal diffusion coefficient of benzene in the vertical barrier wall is 1.56 × 10⁻⁶. -10 m 2 / s, with a longitudinal diffusion coefficient of 8.51×10 -11 m 2 / s.

[0049] Three groundwater monitoring points were set up outside the barrier wall structure to systematically assess the migration and diffusion of pollutants and the barrier effect: Monitoring point 1 was set up laterally on the barrier wall structure as a lateral diffusion monitoring point to monitor the impact of the lateral diffusion of the pollutant plume on the soil and groundwater environment on both sides and to assess its potential risks to surrounding buildings and residential areas; Monitoring point 2 was set up outside the barrier wall and in the direction of the main groundwater flow, adjacent to the barrier wall, as a post-barrier extreme value monitoring point to monitor the peak concentration of pollutants after penetrating the barrier wall and to assess the barrier wall's interception performance and potential breakdown risk; Monitoring point 3 was set up in the downstream area of ​​the main groundwater flow direction outside the barrier wall (i.e., downstream of monitoring point 2) as a downstream impact monitoring point to monitor the impact of the pollutant plume on the downstream soil and groundwater environment and to assess its environmental safety risks to surrounding buildings and residential areas.

[0050] Using COMSOL, a Darcy flow field was established to calculate the seepage path of the pollution plume through the barrier wall in this comparative example. The pollution source concentration follows the natural decay period of benzene of 495 days, and the permeability coefficient of the aquifer outside the pollution source in the plant area is 10. -5 The flow rate was m / s, the porosity was 0.4, and the boundary condition was set at a head difference of 5m between upstream and downstream. Monitoring point 1 was located laterally to the outside of the barrier wall, 20m from the wall and 75m from the center of the wall; monitoring point 2 was located 20m downstream of the center of the wall; and monitoring point 3 was located 100m downstream of the center of the wall. These three monitoring points together formed a lateral-near-downstream monitoring system. The Darcy flow field calculation results are as follows: Figure 3 As shown, when using the traditional pure barrier wall scheme, although the pollution plume behind the inner wall is blocked in the short term, pollutants continue to accumulate, causing the benzene concentration at the downstream monitoring point to remain stable above 0.020 mg / L for a long time, exceeding the Class III limit (0.01 mg / L) of the Groundwater Quality Standard by 100%, which poses a significant environmental risk.

[0051] Example: Under the same background case, the prefabricated bio-permeable reactive barrier wall-barrier wall proposed in this invention is installed. The prefabricated bio-permeable reactive barrier wall-barrier wall combination structure is installed 100m downstream of the plant area, with the wall embedded 1m into the impermeable layer. The length of the prefabricated bio-permeable reactive barrier wall is 50m, and the length of one side of the prefabricated barrier wall (the length from the center of the entire underground continuous wall to both sides, i.e., half the length of the entire underground continuous wall) is 100m. The thickness of both the prefabricated bio-permeable reactive barrier wall and the prefabricated barrier wall is 1m; the permeability coefficient of the prefabricated bio-permeable reactive barrier wall is 6×10⁻⁶. -5 m / s, porosity of 0.5; permeability coefficient of prefabricated barrier wall is 5×10 -11The groundwater flow rate is m / s, and the porosity is 0.35. Three groundwater monitoring points were set up outside the reactive wall-barrier wall composite structure to systematically evaluate the migration and diffusion of pollutants and the barrier effect. The location and function of the three monitoring points were based on the comparative example. Specifically, monitoring point 1 was set up laterally on the composite structure; monitoring point 2 was set up outside the reactive wall and located in the direction of the main groundwater flow, adjacent to the reactive wall, as the extreme value monitoring point behind the reactive wall; monitoring point 3 was set up downstream of monitoring point 2 as the downstream impact monitoring point.

[0052] Other parameters are set as follows: benzene pollution source concentration is 1000 mg / L, and the degradation coefficient of benzene in the aquifer is 10. -9 s -1 The degradation coefficient in the bio-permeable reactive barrier is 10. -5 s -1 The barrier factor for benzene in a bio-permeable reactive barrier is 1; the barrier factor in a vertical barrier is 17.88. The horizontal diffusion coefficient of benzene in a prefabricated bio-permeable reactive barrier is 1.75 × 10⁻⁶. -5 m 2 / s, with a longitudinal diffusion coefficient of 1.58×10 -6 m 2 / s; the horizontal diffusion coefficient in prefabricated barrier walls is 1.56×10⁻⁶. -10 m 2 / s, with a longitudinal diffusion coefficient of 8.51×10 -11 m 2 / s.

[0053] Using COMSOL to establish the Darcy flow field calculation in this embodiment, the pollution plume in the plant area seeps through the prefabricated bio-permeable reactive barrier-barrier structure. The pollution source concentration follows the natural decay period of benzene of 495 days, and the permeability coefficient of the aquifer in the plant area excluding the pollution source is 10. -5 The flow rate is m / s, the porosity is 0.4, and the boundary condition is set to a head difference of 5m between upstream and downstream.

[0054] Darcy flow field calculation results are as follows Figure 4As shown (the arrangement of monitoring points 1, 2, and 3 is the same as in the comparative example), simulation results indicate that under the condition of the barrier wall and reactive wall synergistic system of the present invention, the pollution plume is significantly reduced before reaching the barrier structure. After passing through the prefabricated biopermeable reactive wall-barrier wall, the benzene concentration is significantly reduced to 0.000-0.005 mg / L. Downstream monitoring points only show brief and low-amplitude concentration responses, and their peak concentrations are always lower than the Class III groundwater quality limit (0.01 mg / L). Compared with the pure barrier wall scheme in the comparative example, the downstream concentration is reduced by about 73.9%, and it decays rapidly over time. No pollutant accumulation or secondary increase occurs during long-term operation, indicating that the system can achieve continuous reduction of pollutants while blocking pollution migration.

[0055] Under the combined structure of reactive barrier and barrier walls, pollutants preferentially enter the reactive barrier and react with the packing material due to the reactive barrier's permeability coefficient being approximately six orders of magnitude higher than that of the barrier wall. Most pollutants are degraded or adsorbed and removed during this process. In the example, although monitoring point 3 showed a peak benzene concentration in year 16, its maximum value was only 0.009 mg / L, lower than the Class III groundwater quality limit (0.01 mg / L), and subsequently gradually decreased over time, effectively controlling the downstream environmental risk at a low level. In contrast, although the benzene concentration at monitoring point 3 in the comparative example was low in the early stages, it exceeded 0.01 mg / L after approximately 131.4 years and continued to rise, making it difficult to guarantee the long-term stability of the barrier effect. Overall, the combined reactive barrier and barrier wall structure, through the synergistic effect of "physical barrier + in-situ remediation," is significantly superior to a single barrier wall relying solely on passive blocking, demonstrating clear advantages in the long-term effectiveness of pollution control and environmental safety.

[0056] It will be understood by those skilled in the art that the above descriptions are merely preferred examples of the invention and are not intended to limit the invention. Although the invention has been described in detail with reference to the foregoing examples, those skilled in the art can still modify the technical solutions described in the foregoing examples or make equivalent substitutions for some of the technical features. All modifications and equivalent substitutions made within the spirit and principles of the invention should be included within the scope of protection of the invention.

Claims

1. A prefabricated bio-permeable reactive barrier for contaminated sites, characterized in that, It includes a prefabricated bio-permeable reactive wall and a prefabricated barrier wall set perpendicular to the direction of groundwater flow; the prefabricated bio-permeable reactive wall is arranged in the direction of the main groundwater flow; the prefabricated barrier wall is nested around the prefabricated bio-permeable reactive wall and fixed to the bottom of the impermeable layer. The prefabricated bio-permeable reactive wall is assembled by continuously splicing multiple bio-permeable reactive wall components horizontally and vertically; the prefabricated barrier wall is assembled by continuously splicing multiple barrier wall panel components horizontally and vertically; the horizontal direction is horizontal and the vertical direction is vertical. The bio-permeable reactive wall component is a box with an internal cavity. A geotextile drainage net is arranged on the surface of the box perpendicular to the water flow direction and communicates with the internal cavity. The internal cavity of the box is filled with zero-valent iron-biochar-enhanced / immobilized sulfate-reducing bacteria reactive filler.

2. The prefabricated bio-permeable reactive barrier wall for contaminated sites according to claim 1, characterized in that, The bio-permeable reactive wall component includes: a tenon, a slot, and a geotextile drainage net; the two planes of the box body of the bio-permeable reactive wall component used for horizontal connection are provided with a tenon structure, that is, one plane is provided with a protruding tenon and the other plane is provided with a recessed slot.

3. The prefabricated bio-permeable reactive barrier wall for contaminated sites according to claim 1, characterized in that, The barrier wall panel component includes: two tenons and two slots; the barrier wall panel component is in the form of a rectangular block structure, and its two planes perpendicular to the horizontal direction are also provided with tenon and mortise structures, that is, one plane is provided with a protruding tenon and the other plane is provided with a recessed slot.

4. The prefabricated biopermeable reactive barrier wall for contaminated sites according to claim 1, characterized in that, The materials used in the barrier wall panel components include: slag, polymer-modified bentonite, and geopolymers.

5. The prefabricated biopermeable reactive barrier wall for contaminated sites according to claim 4, characterized in that, The mass ratio of the slag is 55%~85%, the mass ratio of polymer-modified bentonite is 5%~15%, and the mass ratio of geopolymer is 10%~30%.

6. The prefabricated biopermeable reactive barrier wall for contaminated sites according to claim 1, characterized in that, The joints between adjacent bio-permeable reactive wall components, the joints between adjacent barrier wall components, and the joints between bio-permeable reactive wall components and barrier wall components are sealed by injecting calcium-based bentonite slurry.

7. A method for constructing a prefabricated bio-permeable reactive barrier wall for contaminated sites, characterized in that, Includes the following steps: S1: Prepare zero-valent iron-biochar-enhanced / immobilized sulfate-reducing bacteria reactive filler, fill it into the internal cavity of the bio-permeable reactive wall component, and then encapsulate it with geotextile composite drainage net to obtain the bio-permeable reactive wall component. S2: Prepare barrier wall panel components, the materials of which include: slag, polymer-modified bentonite, and geopolymer; in the barrier wall panel components, the mass proportion of slag is 55%~85%, the mass proportion of polymer-modified bentonite is 5%~15%, and the mass proportion of geopolymer is 10%~30%; S3: A channel-type cutting trench is opened downstream of the pollution plume using the channel-type cutting underground continuous wall construction process. S4: Assemble a positioning guide frame for the channel-type cutting groove, and slowly insert the barrier wall panel components or bio-permeable reactive wall components into the channel-type cutting groove and fix them in sequence according to the design drawings, thereby completing the prefabricated bio-permeable reactive wall-barrier wall for contaminated sites as described in any one of claims 1-6.

8. The construction method for prefabricated bio-permeable reactive barrier walls / barrier walls for contaminated sites according to claim 7, characterized in that, In step S1, the zero-valent iron-biochar-enhanced / immobilized sulfate-reducing bacteria reactive packing material is prepared through the following sub-steps: (1.1) Pyrolyze wheat straw at 700-750℃ to form biochar, then sterilize the biochar in an immobilization medium at 120-122℃ for 30-40 min, inoculate sulfate-reducing bacteria at an inoculum concentration of 2%-2.1% by mass, and incubate at 25-30℃ and 120-180 r•min. -1 Under fixed conditions, culture for 18-24 hours; (1.2) Stir the substances in the culture medium at 6000-8000 r•min -1 Centrifuge for 10-15 minutes, discard the supernatant, and wash the lower precipitate with physiological saline. The washed product was centrifuged again at 3000-5000 r / min for 10 min, and the lower precipitate was washed at least 3 times. The resulting solid was the biochar-enhanced / immobilized sulfate-reducing bacteria. (1.3) Biochar-enhanced / immobilized sulfate-reducing bacteria and zero-valent iron are stirred at a mass ratio of 4:1 for 30-40 min at high speed to obtain zero-valent iron-biochar-enhanced / immobilized sulfate-reducing bacteria reactive filler. This filler is then inserted into the internal cavity of the biopermeable reactive wall component, ensuring that the permeability coefficient is greater than 1×10⁻⁶. -3 cm / s.

9. The construction method for prefabricated bio-permeable reactive barrier walls / barrier walls for contaminated sites according to claim 7, characterized in that, In step S2, the barrier wall panel component is prepared through the following sub-steps: (2.1) Mix sodium polyacrylate bentonite and water thoroughly for 30-60 minutes. Seal the resulting sodium polyacrylate bentonite slurry in a container and let it stand until it is completely hydrated. Then add a certain mass of construction waste and stir at 3000 r / min for 30-60 minutes. (2.2) Add magnesium oxide and blast furnace slag to the slurry prepared in step (2.1), and stir for 30-60 minutes to obtain a mixed slurry of slag, polymer-modified bentonite, and geopolymer; pour the mixed slurry into a mold, press it into shape, and then cure it. After standing for 24 hours, the barrier wall panel component is obtained, and its permeability coefficient is less than 1×10. -7 cm / s.

10. The construction method for prefabricated bio-permeable reactive barrier walls / barrier walls for contaminated sites according to claim 7, characterized in that, The aforementioned channel-cutting diaphragm wall construction process is a construction technique that uses a chainsaw to rotate up and down and move horizontally along the pre-set prefabricated bio-permeable reactive wall-barrier wall layout direction to cut channel-cutting grooves in the foundation soil layer.

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